EDP Sciences
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Volume 381, Number 3, January III 2002
Page(s) 862 - 883
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20011469

A&A 381, 862-883 (2002)
DOI: 10.1051/0004-6361:20011469

Three stellar associations and their field east of LMC 4 in the Large Magellanic Cloud

D. Gouliermis1, S. C. Keller2, K. S. de Boer1, M. Kontizas3 and E. Kontizas4

1  Sternwarte der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
2  Institute of Geophysics and Planetary Physics, Lawerence Livermore National Laboratory, 413, PO Box 808, Livermore, CA 94550, USA
3  Department of Astrophysics Astronomy & Mechanics, Faculty of Physics, University of Athens, 157 83 Athens, Greece
4  Institute for Astronomy and Astrophysics, National Observatory of Athens, PO Box 20048, 118 10 Athens, Greece

(Received 20 December 2000 / Accepted 18 October 2001 )

We present photometry in an area of 205 $\times$ 205 centered on LH 95 situated to the north-east of the super-bubble LMC 4. We investigate the stellar content of three stellar associations (LH 91, LH 91-I & LH 95) and their surrounding fields. Our observations use the R-H colour index to identify the Be star population of the region. We find that Be stars exist in all three of the investigated associations. Within LH 95 we find a central cluster of four Be stars which strongly determine the HII emissivity in this area. We estimated the reddening and the age of the systems based on isochrone fitting. The reddening was found to vary between $E(B-V) \simeq 0.15$ and 0.20 mag. All systems were found to be younger than 10 Myr, while the field is older than ~50 Myr. We also present the luminosity and mass functions of the systems, as well as that of the field. It was found that the luminosity function slope s of the field is steeper than that of the systems, which were found to be $s \simeq 0.12$-0.32. The MF slopes were estimated for both systems and field by directly counting stars between evolutionary tracks. We verify that the MF slopes of the systems are rather shallower than the ones of the field. The MF slopes of the systems lie in the range $-1.0 < \Gamma < -2.0$, while those of various fields are significantly steeper, around $\Gamma \simeq -4.0$. LH 95 was found to be probably under disruption. We discuss the possibility that this association is in the process of dissipation.

Key words: Magellanic Clouds -- stars: emission-line, Be -- formation -- C-M diagrams -- luminosity function, mass function -- HII regions -- ISM: individual objects: DEM L 251, DEM L 252 -- open clusters and associations: individual: LH 91, LH 91-I, LH 95

Offprint request: D. Gouliermis, dgoulier@astro.uni-bonn.de

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